Compressor blade root heating system

ABSTRACT

A compressor blade root heating system for a turbine engine is disclosed. The compressor blade root heating system may be formed from one or more induction heaters formed from one or more induction coils positioned in close proximity to a root of a compressor blade. In one embodiment, the induction heater may be coupled to a static casing component positioned immediately upstream of a first row of compressor blades on a rotor assembly such that the induction heater is stationary during turbine engine operation. The induction heater causes eddy current formation, which heats the row one compressor blades. This heating increases the fracture toughness of the material forming the rotor and compressor blades, thereby increasing the mechanical life cycle.

FIELD OF THE INVENTION

This invention is directed generally to turbine engines, and moreparticularly to heating systems in turbine engines.

BACKGROUND

Typically, gas turbine engines include a compressor for compressing air,a combustor for mixing the compressed air with fuel and igniting themixture, and a turbine blade assembly for producing power.

Typically, gas turbine engines start at ambient temperatures, which attimes can be cold, such as five degrees Celsius or below. Cold ambienttemperatures can negatively affect the material properties of thecompressor rotor, limiting the cyclic life of these components.Typically, the row one compressor disk is most affected by cold ambienttemperatures since there is no heating of the gas path prior to thestage. Attempts have been made to increase the life spans of thecompressor components by limiting the start temperatures to higherambient temperatures, by applying more expensive blade materials toreduce blade mass or introduce more expensive disk materials to improvefracture toughness, by applying use of inlet heaters to raise thetemperature of the inlet air, by overspeeding rotation of the rotor tointroduce residual compressive stresses, and by combinations of theseactions. Nonetheless, an efficient and cost effective system is stillneeded.

SUMMARY OF THE INVENTION

This invention relates to a compressor blade root heating system for aturbine engine. The compressor blade root heating system may be formedfrom one or more induction heaters formed from one or more inductioncoils positioned in close proximity to a root of a compressor blade. Inone embodiment, the induction heater may be coupled to a static casingcomponent positioned immediately upstream or downstream of a first rowof compressor blades on a rotor assembly such that the induction heateris stationary during turbine engine operation. The roots of each bladepasses by the induction heater as the rotor assembly rotates. Theinduction heater causes eddy current formation, which heats the row onecompressor blades and rotor disc attachment. This heating increases thefracture toughness of the material forming the rotor disc attachment forthe compressor blades, thereby increasing the mechanical life cyclewithout the cost and performance impact of a conventional inlet airheater or operation restrictions related to ambient temperature.

The turbine engine may include one or more combustors positioneddownstream from a compressor rotor assembly that is positioned within acompressor. The turbine engine may also include a first row ofcompressor blades attached to the compressor rotor assembly, wherein thecompressor blades may each extend radially outward and terminateproximate to inner surfaces of one or more ring segments. The compressorblade may include a root extending radially inward from a platform onthe compressor blade, wherein the root may be configured to attach thecompressor blade to the rotor assembly. The turbine engine may includean induction heater in close proximity to the root of the compressorblade. In at least one embodiment, the compressor blade root heatingsystem may include a plurality of induction heaters.

The induction heater may be stationary during turbine engine operationin which the rotor assembly rotates. The induction heater may beattached to a static casing component positioned immediately upstream ofthe first row of compressor blades. In another embodiment, the inductionheater may include a plurality of induction heaters coupled to thestatic casing component. The induction heater may be formed from one ormore induction coils.

The induction heater may be controlled by controlling the amount ofpower supplied to the induction heater. The heater may be activatedbefore the turbine engine is started to preheat the compressor blade,including the root and rotor disc attachment. If the rotor isstationary, it may be necessary to apply alternating frequency currentto the electromagnets of the induction heater to cause eddy currentformation in the rotor assembly prior to engine start. However, if therotor is rotating due to turning gear operation, application of directcurrent to the electromagnets of the induction heater may be sufficientto cause eddy current formation in the rotor assembly prior to enginestart. Increasing the temperature of the material forming the rotorassembly disc increases the fracture toughness of rotor material.Consequently, the mechanical cyclic life is increased.

An advantage of this invention is that the compressor blade root heatingsystem may effectively increase cyclic life of the turbine airfoil rotorwithout the cost and negative performance characteristics associatedwith a conventional inlet air heater limiting the start temperatures tohigher ambient temperatures, by applying more expensive blade materialsto reduce blade mass or introduce more expensive disk materials toimprove fracture toughness, by applying use of inlet heaters to raisethe temperature of the inlet air, by overspeeding rotation of the rotorto introduce residual compressive stresses, or operation restrictionsrelated to ambient temperature.

These and other embodiments are described in more detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate embodiments of the presently disclosedinvention and, together with the description, disclose the principles ofthe invention.

FIG. 1 is a cross-sectional side view of a portion of the turbineengine.

FIG. 2 is an axial view of a portion of the first row of compressorblades attached to the rotor assembly at detail line 2-2 in FIG. 1.

FIG. 3 is a detailed view of a portion of the turbine engine shown atdetail 3 in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-3, this invention is directed to a compressor bladeroot heating system 10 for a turbine engine 12. The compressor bladeroot heating system 10 may be formed from one or more induction heaters14 formed from one or more induction coils 16 positioned in closeproximity to a root 18 of a compressor blade 20. In one embodiment, theinduction heater 14 may be coupled to a static casing component 23positioned immediately upstream of a first row 24 of compressor blades20 on a rotor assembly 26 such that the induction heater 14 isstationary during turbine engine operation. The induction heater 14causes eddy current 48 formation, which heats the rotor disc attachment22 of the row one compressor blades 20. This heating increases thefracture toughness of the material forming the rotor disc attachment 22,thereby increasing the mechanical life cycle without the cost andperformance impact of an inlet air heater, by applying more expensiveblade materials to reduce blade mass or introduce more expensive diskmaterials to improve fracture toughness, by applying use of inletheaters to raise the temperature of the inlet air, by overspeedingrotation of the rotor to introduce residual compressive stresses, oroperation restrictions related to ambient temperature.

In at least one embodiment, as shown in FIG. 1, the turbine engine 12may include a rotor assembly 26 positioned radially inward from a vanecarrier 28 and the compressor vanes 30. The rotor assembly 26 mayinclude a first row 24 and a second row 36 of compressor blades 20extending radially outward from the rotor assembly 26 and terminatingproximate to inner surfaces 40 of one or more ring segments 42. As shownin FIG. 1, the compressor blades 20 may be assembled into a plurality ofrows, which are also referred to as stages, in addition to the first andsecond rows 24, 36. The compressor blades 20 may have any appropriateconfiguration and may be at least partially formed from an appropriatemetal.

The turbine engine 12 may also include one or more combustors positioneddownstream from the compressor rotor assembly 26. The compressor rotorassembly 26 may be contained within the compressor 34. The rotorassembly 26 may be configured to enable the rotor assembly 26 to rotaterelative to the vane carrier 28, compressor vanes 30 and the staticcasing component 23 positioned upstream from the row one 24 compressorblades 20.

The compressor blade root heating system 10 may include one or moreinduction heaters 14 positioned in close proximity to the root 18 of thecompressor blade 20 to create eddy currents 48 therein. The inductionheater 14 may be stationary during turbine engine operation in which therotor assembly 26 rotates. In at least one embodiment, the inductionheater 14 may be attached to the static casing component 23 positionedimmediately upstream of the first row 24 of compressor blades 20. Inother embodiments, the induction heater 14 may be attached to otherstructures. In one embodiment, the compressor blade root heating system10 may include a plurality of induction heaters 14 coupled to the staticcasing component 23.

The induction heater 14 may be formed from at least one induction coil16. The induction coil 16 may be configured to produce heating in theroot 18 of the compressor blade 20, which is formed at least partiallyof metal, by electromagnetic induction in which eddy currents 48 aregenerated within the metal and by resistance in the metal that causesJoule heating of the material. The induction heater 14 may include anelectromagnet through which a high-frequency alternating current ordirect current is passed. The frequency of the alternating current thatis used depends on numerous factors, including, but not limited to:rotor rotation speed, ambient temperature, the penetration depth, typeof material forming the rotor disc attachment 22, the size of theobject, and how that induction coil 16 is coupled to the object to beheated.

The compressor blade root heating system 10 may also include a method ofheating the rotor disc attachment 22. The method may include providing aturbine engine 12 having the elements set forth above, including, butnot limited to one or more combustors, a compressor 34, a first row 24of compressor blades 20 attached to a rotor assembly 26 positioned inthe compressor 34, one or more blades 20 including a root 18 extendingradially inward from a platform 38 on the compressor blade 20, whereinthe root 18 may be configured to attach to the compressor blade 20 onthe rotor assembly 26, and one or more induction heaters 14 in closeproximity to the root 18 of the compressor blade 20. The method of mayfurther include generating a magnetic field with the induction heater14. The degree of heating of the rotor disc attachment 22 may becontrolled by controlling the amount of power provided to the inductionheater 14, such as by controlling the amount of eddy current 48 createdby the induction heater 14.

The induction heater 14 may create a magnetic field in the region of thecompressor blade attachment, such as the root 18. The magnetic field maycause eddy electrical currents 48 to be generated in the metallicmaterial of the blade root 18 and compressor disk. The rotation of therotor assembly 26 in this magnetic field may help induce the eddycurrent production. This electrical current may cause a rise in themetal temperature due to the electrical resistance of the material. Eddycurrents tend to concentrate near geometric concentrations 44. As shownin FIG. 3, the location of stress concentration in the root 18 whichlimits the fracture mechanic critical crack size and thus limitingcyclic life or minimum starting temperature is shown at 44. The locationof maximum heating from the induction heater 14 is at points 46 due tocrowding (high density) of eddy-currents 48. Thus, the heating effect isconcentrated at the same locations which have the limiting fracturemechanic critical size and thus limiting cyclic life or minimum startingtemperature. Preheating the rotor disc attachment 22 enables thecritical crack size to be increased, thereby enabling the correspondingfracture mechanic cyclic life to be increased.

The foregoing is provided for purposes of illustrating, explaining, anddescribing embodiments of this invention. Modifications and adaptationsto these embodiments will be apparent to those skilled in the art andmay be made without departing from the scope or spirit of thisinvention.

1. A turbine engine formed from a compressor including a rotor assembly,the turbine engine comprising: a row of compressor blades attached tothe rotor assembly, wherein the compressor blades each extend radiallyoutward, wherein at least one compressor blade includes a root extendingradially inward from a platform on the compressor blade, the rootconfigured to attach the at least one compressor blade to the rotorassembly; at least one induction heater in close proximity to the rootof the at least one compressor blade.
 2. The turbine engine of claim 1,wherein the at least one induction heater is stationary during turbineengine operation in which the rotor assembly rotates.
 3. The turbineengine of claim 2, wherein the at least one induction heater is attachedto a static casing component positioned immediately upstream of the rowof compressor blades.
 4. The turbine engine of claim 3, wherein the atleast one induction heater comprises a plurality of induction heaterscoupled to the static casing component.
 5. The turbine engine of claim1, wherein the at least one induction heater comprises a plurality ofinduction heaters coupled to the static casing component.
 6. The turbineengine of claim 1, wherein the at least one induction heater is formedfrom at least one induction coil.
 7. A turbine engine formed from acompressor including a rotor assembly, the turbine engine comprising: arow of compressor blades attached to the rotor assembly, wherein thecompressor blades each extend radially outward, wherein at least onecompressor blade includes a root extending radially inward from aplatform on the compressor blade, the root configured to attach the atleast one compressor blade to the rotor assembly; at least one inductionheater formed from at least one induction coil positioned in closeproximity to the root of the at least one compressor blade and coupledto a static casing component positioned immediately upstream of the rowof compressor blades such that the at least one induction coil isstationary during turbine engine operation.
 8. The turbine engine ofclaim 7, wherein the at least one induction heater comprises a pluralityof induction heaters coupled to the static casing component.
 9. A methodof heating a compressor blade of a turbine engine, comprising: providinga turbine engine formed from a compressor including a rotor assembly,the turbine engine comprising: a row of compressor blades attached tothe rotor assembly, wherein the compressor blades each extend radiallyoutward, wherein at least one compressor blade includes a root extendingradially inward from a platform on the compressor blade, the rootconfigured to attach the at least one compressor blade to the rotorassembly; at least one induction heater in close proximity to the rootof the at least one compressor blade; and generating a magnetic fieldwith the at least one induction heater.
 10. The method of claim 9,wherein further comprising rotating the rotor assembly to assist in eddycurrent production.
 11. The method of claim 9, wherein providing aturbine engine comprises providing a turbine engine wherein the at leastone induction heater is stationary during turbine engine operation inwhich the rotor assembly rotates.
 12. The turbine engine of claim 11,wherein providing a turbine engine comprises providing a turbine enginewherein the at least one induction heater is attached to a static casingcomponent positioned immediately upstream of the row of compressorblades.
 13. The turbine engine of claim 12, wherein providing a turbineengine comprises providing a turbine engine wherein the at least oneinduction heater comprises a plurality of induction heaters coupled tothe static casing component.
 14. The turbine engine of claim 9, whereinproviding a turbine engine comprises providing a turbine engine whereinthe at least one induction heater comprises a plurality of inductionheaters coupled to the static casing component.
 15. The turbine engineof claim 9, wherein providing a turbine engine comprises providing aturbine engine wherein the at least one induction heater is formed fromat least one induction coil.